Monitoring device for polyphase power supply systems



E. A. BOURDEAU MONITORING DEVICE FOR POLYPHASE POWER SUPPLY SYSTEMS Dec. 16, 1958 Filed April 21, 1958 United States Patent MONITORING DEVICE FGR POLYPHASE POWE SUPPLY SYSTEMS Eusbe A. Bourdeau, Nanterre, France, assignor to La T elemecanique Electriqne (Societe Anonyme), Nanterre, France, a company of France Application April 21, 1958, Serial No. 729,705

Claims priority, application France May 3, 1957 8 Claims. (Cl. 200116) This invention relates to monitoring devices for polyphase alternating-current supply systems, and more especially to such monitoring devices operating by thermal action.

A known form of polyphase monitoring device comprises a set of bimetallic temperature-responsive members one for each phase of the supply system to be monitored, said bimetal members being arranged in parallel coplanar relation, and a common control means, such as a cut-off switch, operated by said bimetal members through suitable leverage mechanism, the arrangement being such that said control means or switch is operated both in the event that all the bimetal members are simultaneously flexed by amounts greater than predetermined values, thereby indicating that all the phases of the system are overloaded, and also in the event that any one or more of the bimetal members has been flexed by a greater amount than the remaining members, which would be indicative of a condition of unbalance between the phases.

In prior devices of this character the bimetal strip members are connected to the control means, such as a cut-off switch, through levers pivoted to brackets, clevises or the like, carried by the bimetal strips and the resulting mechanical linkages are complicated and unreliable, increasing construction and maintenance costs.

Objects of this invention are to provide an improved and simplified monitoring device of the type specified, to provide increased sensitivity of response to a condition of unbalance and differential flexing of the bimetal members, and further to ensure accurately the same sensitivity in response to differential flexing of any one of the bimetal strip members.

In accordance with the invention there is provided a' monitoring device for a polyphase power system, comprising a set of bimetal members equal in number to the system phases and arranged in parallel spaced relation in a common plane to flex away from said plane in response to temperature variations as determined by variations in current flow in the respective phases, a platelike element associated with the, or each, pair of adjacent ones of said bimetal members and extending in a plane normal to said common plane and in a direction transverse to said members, said or each said element including a portion extending betwen said pair of members, means pivotally connecting opposite sides of said portion to adjacent sides of the respective members of said pair, at least one of said connecting means, and preferably each one thereof, comprising a cutout in said portion with the sides of the cutout in substantially point-contact engagement with opposite faces of said adjacent side of the related member, said element further including side arms projecting from opposite sides of it outside said common plane beyond said pivotal connecting means, current control means, e. g. switch means, displaceable for controlling current flow in said system and including actuator portions operably engageable by each of said arms, and guide means constraining said, or each said, element for movement in said normal plane, whereby equal flexing of by means of end pivot pins 2a.

. 10 disposed in a common general plane.

2,864,915 Patented Dec. 1 6, 1958 said bimetal members will bodily displace said element, or all said elements, while differential flexing of said members will tilt said element, or at least one of said elements, to actuate said actuator portion and displace said current control means.

A clear understanding of the invention will be had from a perusal of the ensuing description which relates to exemplary, non-restrictive embodiments thereof, with refermeans connecting the bimetal strips with the commoncurrent control device;

Fig. 4c is an enlarged view on the section line IVIV of Fig. 2;

Fig. 5 illustrates a modified form of pivoting notch means, and

Fig. 6 is a perspective view of a modified pivotal arrangement for the connection between the plates and bimetal strips.

The control or monitoring device ill-ustratedrby way of example is designed for a three-phase power network and comprises three parallel spaced bimetal strips 1a, 1b, The three strips may be connected so as to be traversed by current from the three phases of the network respectively, or, more preferably, the bimetal strips may be indirectly heated by small resistant heater elements, not shown, of equal resistance value, arranged in heat exchange relation with the respective strips and connected in series with the phase lines of the supply system.

The common current control unit or switch comprises herein a conductive bar 2 pivoted about the axis XX the contacts 3 and 4 upon predetermined distortion of the bimetal strips as further described.

The leverage means of the invention comprises a pair of identical plates 6 each formed with two notches or cutouts 6a embracing the adjacent edges of two adjacent bimetal strips, and two side arms or extensions 6b equal and symmetrically arranged for engagement with the vanes 5.

Disposed between the bimetal strips are separating members 7 made of insulating material which serve to provide electrical separation between the bimetal strips, and said elements 7 are formed with slots 7a therein extending perpendicularly to the planes of the bimetal elements, which slots receive the plates 6 therein. The slots serve to guide the plates preventing movement thereof out of their plane. The device operates as follows:

When the three phase conductors of the supply network have equal currents flowing therein all three bimetal strips are equally heated and flex tothe same extent. Hence the three bimetal strips remain in a common plane and the strips 6 areheld in a relative position as shown in Fig. ,2, i. e. the uppermost surfaces of all three strips are coplanar, or'flat. 3 Hence,

The bar has secured T 3 upward displacement ofthe vanes 5 to a degree sulficient to disengage the contacts 3 and 4, can only occur if all three bimetal strips are simultaneously flexed by amounts greater than a prescribed amount as determined by adjustment of the contacts.

However, should the current flowing through one of the network phases be substantially higher than that through the other phases the corresponding bimetal strip is differentially flexed relatively to the others and one of the plates 6 is tilted, so that one of the extensions 6b is raised and now acts directly on a flap 5, as shown in Fig. 3, to disengage the switch contacts 34.

To increase the sensitivity of the device and ensure switch response to small ditferential deformation of the bimetal strips, it is desirable to increase the length of the extensions 6b with respect to the spacing between the notches 6a of the plate, that is, referring to Fig. 2, the distance B should be selected greater than A. Since there is nothing to prevent both increasing the length of the side extensions 6!; and reducing the spacing of the notches 6a, to any reasonable degree, it will be seen that the sensitivity of the device can be made very great so as to respond to minute degrees of unbalance between the phase load current.

Moreover it will be readily apparent from Figs. 2 and 3 that a given differential flexing between any two bimetal strips will cause the same amount of displacement of the vanes 5, and hence the sensitivity of the device will be the same in respect to each of the three phases.

However it will also be seen that in the construction shown, because of the unavoidable small transverse offset present between the juxtaposed plates 6, a slight difference may exist as between the leverages of the forces applied by the two plates 6 upon the bimetal strips, as measured from the axis X-X. To avoid this, as shown in Fig 4c, the edges of the strips 6 around the notches 6a and extension arms 6b are bevelled in opposite directions as between the two plates, so that the points of engagement of both plates 6 both with the bimetal strips 1a, 1b, 1c, and with the vanes 5, will lie in a common plane parallel to the axis XX in each of the plates 6. Such bevelled configuration further facilitates smooth frictionless sliding movement of the bimetal strips and the vanes relatively to the plates 6; this relative sliding movement is due to the fact that the plates are able to move only in the slots 7:: whereas the vanes and bimetal strips perform a longitudinal displacement relative to the plates, as a result, respectively, of the rotation of the vanes about the axis X-X, and the arcuate shape assumed by the bimetal strips on Both in the embodiment illustrated in Fig. l and that in Fig 4b, the vanes 5 and the bimetal strips are arranged for rotation in opposite directions. This however is not essential and the invention, as shown in Fig. 4a, makes it possible if desired so to arrange the bimetal strips and the vanes that they will rotate in the same directions, as indicated by the arrows. Such an arrangement may in fact enable the device to be constructed to a smaller over-all size than the first arrangement described.

In the embodiment of the invention described the nose portions of the plates 6 which define the sides of each notch 6a and engage the sides of the bimetal strips may tend to be somewhat delicate and easily breakable since the plates 6 are made of insulating material and said nose portions are, moreover, reduced in thickness in the direction normal to the plane of the plates owing to the bevels mentioned above. This difliculty may be overcome as shown in Fig. 5 where the sides of the notches 6a are formed with straight parallel edges as shown at 66, and each bimetal strip such as has hearing elements 8 bonded to it on each side, and extending in a general direction normal to the sides 60 of the notch. The bearing elements 8 are preferably formed 4 l with semi-cylindrical surfaces as shown in order to avoid damage to the sides 60 of the notch and permit ready sliding engagement with respect thereto in case of differential flexing of the bimetal strips.

An advantage of the notch-type pivotal connection according to the invention is that it will allow for free differential flexing of the bimetal strips without imparting twisting stresses thereto; this however necessarily entails the need that the plates 6 should be able to assume a small degree of displacement transversely to the bimetal strips within the slots 7. This require ment may be troublesome in cases where the walls of the casing surrounding the device lie in very close proximity to the ends of the outwardly directed extensions 6b of the plates, since the ends of such extensions will be liable to engage said walls and the resulting friction will interfere with the proper operation of the device. This difficulty can be overcome by the provision of guiding means for the plates which will restrict transverse displacements thereof. Thus, as shown in Fig. 6, the central bimetal strip 1b may be offset somewhat to the rear of the other two bimetal strips 1a and 1c and has spaced pivot pins 9 projecting from it into an aperture formed in each plate 6. The other side of each plate is pivoted through a notched arrangement as previously described to the side of the adjacent bimetal strip 1a and 10, as shown. This prevents transverse movement of the plates and prevents the arms 6b from frictionally engaging the wall surfaces of the casing without increasing the overall size of the device.

It will be understood that various modifications may be madein addition to those explicitly described and illustrated without exceeding the scope of the present invention. Thus, while the monitoring devices shown relate to a three-phase supply system, the changes to be introduced therein in cases when the invention is to be applied to a two-phase, or a fouror more-phase power supply system, will be readily apparent to anyone familiar with the art.

What I claim is:

1. In a polyphase power system monitoring device of the type described, at least a pair of coplanar, parallel spaced bimetal strips adapted to flex out of their common plane in response to current flow in related phases of the system, at least one platelike element positioned in a plane normal to said common plane and transverse to said strips, said element having opposite side notches embracing adjacent side edges of the respective strips, side arms projecting from opposite sides of said element beyond said notches and lying outside said common plane, guide means constraining said element to movement in said normal plane, and means displaceable for controlling current in said system including actuator portions actuable by said side arms, whereby equal flexing of said strips will bodily displace said element, while differential flexing of said strips will tilt said element in said normal plane, to actuate said actuator portions for displacing said control means.

2. In a polyphase system monitoring device of the type described, at least a pair of coplanar, parallel spaced bimetal strips adapted to flex out of their common plane in response to current flow in related phases of the system, a platelike element positioned in a plane normal to said common plane and transverse to said strips, means pivotally connecting opposite side portions of said element with adjacent side edges of said respective strips, at least one of said connecting means comprising a cutout in said element side portion having the sides of said cutout in substantially point-contact engagement with opposite faces of the adjacent side edge of a strip, side arms projecting from opposite sides of said element beyond said strips and lying outside of the common plane thereof, non-pivotal guide-means constraining said element to movement in said normal plane only, and means displaceable for controlling current flow in said system ineluding actuator portions engageable by said arms, whereby both equal and differential flexing of the strips will displace said element in its said normal plane for displacing said control means.

3. In a monitoring device for a polyphase power system, a set of bimetal members equal in number to the system phases and arranged in parallel spaced relation in a common general plane to flex away from said plane in response to temperature variations, means controlling the temperature of each member in accordance with the current in a related phase, common current control means displaceable for controlling the current flow in said system phases, a platelike element associated with a pair of adjacent members and extending in a plane normal to said common plane and in a direction transverse to said members, said element including a portion extending between said pair of members, means pivotally connecting opposite sides of said portion to adjacent sides of said respective members, at least one of said connecting means comprising a notch in said portion having the sides of said notch in substantially point contact engagement with opposite faces of said adjacent side of the member, said element further including side extension arms projecting from opposite sides thereof outside the common plane of said members beyond said connecting means, actuating means connected to said control means and operably engageable by each of said arms, and guide means constraining said element to displacement in said normal plane, whereby equal flexing of said members will bodily displace said element, while diflerential flexing of said members Will tilt said element, to operate said actuating means and displace said common control means.

4. In a monitoring device of the type described for a three-phase power system, three coplanar parallel spaced bimetal strips adapted to flex out of their common plane in response to current flow in related phases of the system, two platelike elements positioned in closely-adjacent planes normal to said common plane and transverse to said strips, each element having a portion intermediate two adjacent ones of said three strips, and two opposite side arms projecting from opposite sides of each element outside said common plane, opposite cutouts formed in the intermediate portion of each element each cutout embracing between the sides thereof a side edge portion of one of said strips, guide means constraining said elements to movement in said normal planes and common means displaceable for controlling current flow in said system including actuator portions actuable by said side arms, whereby equal flexing of said strips will bodily displace both said elements, while differential flexing of the strips will tilt at least one of said elements, to actuate said actuator portions for displacing said common control means.

5. In a monitoring device of the type described for a three-phase power system, three coplanar parallel spaced bimetal strips adapted to flex out of their common plane in response to current fiow in related phases of the system, two platelike elements positioned in closely-adjacent planes normal to said common plane and transverse to said strips, a cutout formed in an outer side of each element with the sides of said cutout in point-contact engagement with opposite faces of the inner side edge portion of a respective outermost one of said three strips, an aperture formed in the opposite side of each element and spaced pins projecting from a middle one of said strips into rotatable engagement with the apertures in said respective elements whereby each element is pivotally connected to two adjacent ones of said three strips, each element further including side arms projecting from opposite sides of the element outside said common plane, slotted guide means constraining said elements for movement in said normal planes, and switch means displaceable to a cutoff position for cutting off current flow in said system said switch means including actuator portions engageable by said side arms, whereby equal flexing of the strips will bodily displace both said elements, while difierential flexing of the strips will tilt at least one of said elements, to actuate said actuator portions for displacing said switch means to cutofl position.

6. A device as claimed in claim 4, wherein said elements have bevelled edge portions in contact engagement with said strips and said actuator portions, so arranged that the points of engagement are positioned in a substantially common plane normal to the common plane of said strips.

7. A device as claimed in claim 3, wherein said notch has straight parallel spaced side edges and said adjacent side of said member has bearing surfaces on said opposite faces thereof for substantially point-contact engagement with said side edges of thenotch.

8. A device as claimed in claim 3, wherein said guide means comprise a flange extending between the adjacent bimetal members in a plane normal to said common plane longitudinally of said members, and a slot in said flange slidably and tiltably receiving said element therein.

References Cited in the file of this patent UNITED STATES PATENTS 1,910,494 OKeefe May 23, 1933 2,581,882 Randall Jan. 8, 1952 2,713,623 Bordeau July 19, 1955 2,797,277 Dorfman et al. June 25, 1957 FOREIGN PATENTS 624,957 Great Britain June 20, 1949 

